What is true about proportions? Select all that apply. (Just keep in mind that this is for chemistry class, when trying to find the mass or volume of a substance in an equation.)

A- Proportions are the amount of a substance that contains 6.02 x 1023 particles.

B- Proportions have cross products that are equal.

C- Proportions can be written as equal fractions.

D- Proportions are sums that compare compounds.